Ferroelectric ceramic composition

ABSTRACT

A ferroelectric ceramic composition of a ternary system solid solution represented by the general formula: 
     
         xPb(Sn.sub.αSb.sub.1.sub.-.sub.α)O.sub.3 -- yPbTiO.sub.3 -- 
    
      zPbZrO 3   
     wherein x, y and z are the respective mol fractions of the components, x + y + z = 1.00 and 1/4 ≦ α ≦ 3/4.

This invention relates to ferroelectric ceramic compositions of aternary system Pb(Sn.sub.αSb₁ ₋.sub.α)O₃ --PbTiO₃ --PbZrO₃ which isstable in piezoelectric characteristics.

It is known that ceramic compositions of the system PbTiO₃ --PbZrO₃exhibit desirable piezoelectric characteristics useful for use aspiezoelectric ceramic materials, and various kinds of modified ceramicshave been reported. These ceramic materials are roughly divided into twomain groups, i.e., a hard type and a soft type. One of therepresentatives of the hard type is a ceramic material of the systemPbTiO₃ --PbZrO₃ containing Mn, Fe or Ni and that of the soft type is aceramic material of the system PbTiO₃ --PbZrO₃ containing Nb or Sb.These ceramic materials exhibit desirable piezoelectric characteristics,but the ceramic materials of the soft type have advantages such as thatthe aging thereof is extremely great. For example, if a ceramic materialof the soft type was compulsorily exposed to heat aging at 150°C, itspiezoelectric characteristics such as the electromechanical couplingcoefficient kp deteriorate greatly in proportion to the repeated timesof application of the heat aging. It is therefore considerably difficultto obtain ceramic products having desired characteristics, for example,such as ceramic filters for the objective frequency.

It is therefore an object of the present invention to provideferroelectric ceramic compositions of which the aging is very smallwhile they are of the soft type.

According to this invention, there is provided a ferroelectric ceramiccomposition of a ternary system Pb(Sn.sub.αSb₁ ₋.sub.α)O₃ --PbTiO₃--PbZrO₃ comprising a solid solution represented by the general formula:

    xPb(Sn.sub.αSb.sub.1.sub.-.sub.α)O.sub.3 --yPbTiO.sub.3 --zPbZrO.sub.3

wherein

x + y + z = 1.00

1/4 ≦ α ≦ 3/4

Said composition being in a polygonal area defined by the points A, B,C, D, E and F in FIG. 1, the sets of mol fractions of the threecomponents at said points being as follows:

            x         y           z                                               ______________________________________                                        A         0.01        0.60        0.39                                        B         0.01        0.30        0.69                                        C         0.15        0.25        0.60                                        D         0.25        0.25        0.50                                        E         0.25        0.50        0.25                                        F         0.15        0.60        0.25                                        ______________________________________                                    

If the value of α is less than 1/2, several problems arise along withit. It is therefore preferred to limit the compositional area inresponse to the value of α as follows:

When 1/3 ≦ α < 1/2, it is preferred to limit the compositional area to apolygonal area defined by the points A, B, C, D₁, E₁, and F in FIG. 1,the sets of mol fractions of the three components at said points beingas follows:

             x        y          z                                                ______________________________________                                        A          0.01       0.60       0.39                                         B          0.01       0.30       0.69                                         C          0.15       0.25       0.60                                         D.sub.1    0.20       0.25       0.55                                         E.sub.1    0.20       0.55       0.25                                         F          0.15       0.60       0.25                                         ______________________________________                                    

When 1/4 ≦ α < 1/3, it is preferred to limit the compositional area to apolygonal area defined by the points A, B, C, D₂, E₂ and F in FIG. 1,the sets of mol fractions of the three components at said points beingas follows:

    x              y          z                                                   ______________________________________                                        A       0.01       0.60       0.39                                            B       0.01       0.30       0.69                                            C       0.15       0.25       0.60                                            D.sub.2 0.15       0.35       0.50                                            E.sub.2 0.15       0.50       0.35                                            F       0.15       0.60       0.25                                            ______________________________________                                    

The piezoelectric ceramics according to the invention may be prepared ina manner conventionally adapted for the preparation of piezoelectricceramics.

The piezoelectric ceramics which are the compositions of a ternarysystem Pb(Sn.sub.αSb₁ ₋.sub.α)O₃ --PbTiO₃ --PbZrO₃ have high resistanceto heat aging, in other words, high thermostability in piezoelectriccharacteristics such as electromechanical coupling coefficient(kp),mechanical quality factor (Qm) and dielectric constant(ε_(s)). Inaddition, if they are applied to energy trapped mode ceramic resonators,the difference (Δf) between the antiresonance frequency (fa) andresonance frequency (fo) varies scarcely. Moreover, the temperaturecoefficients (TC) of the antiresonance and resonance frequencies of thepiezoelectric ceramics are small in wide compositional area. Thus, theseceramics according to the present invention are suitable for use asceramic filters, vibrators, acoustic elements, piezoelectric ignitionelements and the like.

The invention will be further apparent from the following descriptionwith reference to examples and the accompanying drawings, in which:

FIG. 1 is a triangular diagram showing the area of the ferroelectricceramic compositions according to the invention;

FIGS. 2 through 7 are the graphs showing the changes of the temperaturecoefficient of frequencies (from -20°C to +80°C) as a function of molarratio of PbTiO₃ /PbZrO₃ ; and

FIG. 8 is a graph showing the relation between the contents of Sn, Sband the degree of sintering.

EXAMPLES

The compounds PbO (or Pb₃ O₄), SnO₂, Sb₂ O₃, TiO₂ and ZrO₂ were used asraw materials. These raw materials were individually weighed to obtain amixture having the compositional proportions shown in Table 1, and thenmixed by the wet process for about 20 hours. After drying, the resultantmixture was presintered at about 750° - 850°C for 2 hours. Thepresintered body was milled by the wet process with a suitable organicbinder for 10 to 20 hours, dried and passed through as 80 mesh sieve toobtain minus sieve powder. The thus obtained powder was molded into adisk with a diameter of 22 mm and a thickness of 1.2 mm at a pressure of750 - 1000 kg/cm² and then sintered at a temperature of 1150° - 1250°Cfor 2 hours in order to obtain a sample of the piezoelectric ceramics.

                  Table 1                                                         ______________________________________                                        Sample      Composition (Mol fraction)                                        No.             α  x      y      z                                      ______________________________________                                        1      *        1        0.03   0.44   0.53                                   2      *        1        0.03   0.46   0.51                                   3      *        1        0.03   0.48   0.49                                   4      *        1        0.03   0.50   0.47                                   5      *        1        0.05   0.44   0.51                                   6      *        1        0.05   0.46   0.49                                   7      *        1        0.05   0.48   0.47                                   8      *        1        0.05   0.50   0.45                                   9      *        1        0.10   0.44   0.46                                   10     *        1        0.10   0.46   0.44                                   11     *        1        0.10   0.48   0.42                                   12     *        1        0.10   0.50   0.40                                   13     A        3/4      0.01   0.60   0.39                                   14     B        3/4      0.01   0.30   0.69                                   15              3/4      0.03   0.44   0.53                                   16              3/4      0.03   0.50   0.47                                   17              3/4      0.05   0.44   0.51                                   18              3/4      0.05   0.50   0.45                                   19              3/4      0.10   0.44   0.46                                   20              3/4      0.10   0.50   0.40                                   21     C        3/4      0.15   0.25   0.60                                   22     F        3/4      0.15   0.60   0.25                                   23     D        3/4      0.25   0.25   0.50                                   24     E        3/4      0.25   0.50   0.25                                   25     A        2/3      0.01   0.60   0.39                                   26     B        2/3      0.01   0.30   0.69                                   27              2/3      0.01   0.44   0.55                                   28              2/3      0.01   0.46   0.53                                   29              2/3      0.01   0.48   0.51                                   30              2/3      0.01   0.50   0.49                                   31              2/3      0.03   0.44   0.53                                   32              2/3      0.03   0.46   0.51                                   33              2/3      0.03   0.48   0.49                                   34              2/3      0.03   0.50   0.47                                   35              2/3      0.05   0.44   0.51                                   36              2/3      0.05   0.46   0.49                                   37              2/3      0.05   0.48   0.47                                   38              2/3      0.05   0.50   0.45                                   39              2/3      0.06   0.44   0.50                                   40              2/3      0.06   0.46   0.48                                   41              2/3      0.06   0.48   0.46                                   42              2/3      0.06   0.50   0.44                                   43              2/3      0.08   0.44   0.48                                   44              2/3      0.08   0.46   0.46                                   45              2/3      0.08   0.48   0.44                                   46              2/3      0.08   0.50   0.42                                   47              2/3      0.10   0.44   0.46                                   48              2/3      0.10   0.46   0.44                                   49              2/3      0.10   0.48   0.42                                   50              2/3      0.10   0.50   0.40                                   51     C        2/3      0.15   0.25   0.60                                   52     F        2/3      0.15   0.60   0.25                                   53     D        2/3      0.20   0.25   0.55                                   54     E        2/3      0.20   0.55   0.25                                   55     A        1/2      0.01   0.60   0.39                                   56     B        1/2      0.01   0.30   0.69                                   57              1/2      0.02   0.42   0.56                                   58              1/2      0.02   0.44   0.54                                   59              1/2      0.02   0.46   0.52                                   60              1/2      0.02   0.48   0.50                                   61              1/2      0.02   0.50   0.48                                   62              1/2      0.03   0.42   0.55                                   63              1/2      0.03   0.43   0.54                                   64              1/2      0.03   0.44   0.53                                   65              1/2      0.03   0.45   0.52                                   66              1/2      0.03   0.46   0.51                                   67              1/2      0.03   0.47   0.50                                   68              1/2      0.03   0.48   0.49                                   69              1/2      0.03   0.49   0.48                                   70              1/2      0.03   0.50   0.47                                   71              1/2      0.03   0.51   0.46                                   72              1/2      0.03   0.52   0.45                                   73              1/2      0.04   0.42   0.54                                   74              1/2      0.04   0.44   0.52                                   75              1/2      0.04   0.46   0.50                                   76              1/2      0.04   0.48   0.48                                   77              1/2      0.04   0.50   0.46                                   78              1/2      0.05   0.42   0.53                                   79              1/2      0.05   0.43   0.52                                   80              1/2      0.05   0.44   0.51                                   81              1/2      0.05   0.45   0.50                                   82              1/2      0.05   0.46   0.49                                   83              1/2      0.05   0.47   0.48                                   84              1/2      0.05   0.48   0.47                                   85              1/2      0.05   0.49   0.46                                   86              1/2      0.05   0.50   0.45                                   87              1/2      0.05   0.51   0.44                                   88              1/2      0.05   0.52   0.43                                   89              1/2      0.06   0.42   0.52                                   90              1/2      0.06   0.44   0.50                                   91              1/2      0.06   0.46   0.48                                   92              1/2      0.06   0.48   0.46                                   93              1/2      0.06   0.50   0.44                                   94              1/2      0.10   0.44   0.46                                   95              1/2      0.10   0.46   0.44                                   96              1/2      0.10   0.48   0.42                                   97              1/2      0.10   0.50   0.40                                   98     C        1/2      0.15   0.25   0.60                                   99     F        1/2      0.15   0.60   0.25                                   100    D        1/2      0.25   0.25   0.50                                   101    E        1/2      0.25   0.50   0.25                                   102    A        1/3      0.01   0.60   0.39                                   103    B        1/3      0.01   0.30   0.69                                   104             1/3      0.01   0.44   0.55                                   105             1/3      0.01   0.46   0.53                                   106             1/3      0.01   0.48   0.51                                   107             1/3      0.01   0.50   0.49                                   108             1/3      0.03   0.44   0.53                                   109             1/3      0.03   0.46   0.51                                   110             1/3      0.03   0.48   0.49                                   111             1/3      0.03   0.50   0.47                                   112             1/3      0.05   0.44   0.51                                   113             1/3      0.05   0.46   0.49                                   114             1/3      0.05   0.48   0.47                                   115             1/3      0.05   0.50   0.45                                   116             1/3      0.06   0.44   0.50                                   117             1/3      0.06   0.46   0.48                                   118             1/3      0.06   0.48   0.46                                   119             1/3      0.06   0.50   0.44                                   120             1/3      0.08   0.44   0.48                                   121             1/3      0.08   0.46   0.46                                   122             1/3      0.08   0.48   0.44                                   123             1/3      0.08   0.50   0.42                                   124             1/3      0.10   0.44   0.46                                   125             1/3      0.10   0.46   0.44                                   126             1/3      0.10   0.48   0.42                                   127             1/3      0.10   0.50   0.40                                   128    C        1/3      0.15   0.25   0.60                                   129    F        1/3      0.15   0.60   0.25                                   130    D.sub.1  1/3      0.20   0.25   0.55                                   131    E.sub.1  1/3      0.20   0.55   0.25                                   132    A        1/4      0.01   0.60   0.39                                   133    B        1/4      0.01   0.30   0.69                                   134             1/4      0.03   0.44   0.53                                   135             1/4      0.03   0.50   0.47                                   136             1/4      0.05   0.44   0.51                                   137             1/4      0.05   0.50   0.45                                   138    C        1/4      0.15   0.25   0.60                                   139    F        1/4      0.15   0.60   0.25                                   140             1/4      0.15   0.44   0.46                                   141             1/4      0.15   0.50   0.40                                   142    D.sub.2  1/4      0.15   0.35   0.50                                   143    E.sub.2  1/4      0.15   0.50   0.35                                   144    *        0        0.03   0.44   0.53                                   145    *        0        0.03   0.46   0.51                                   146    *        0        0.03   0.48   0.49                                   147    *        0        0.03   0.50   0.47                                   148    *        0        0.05   0.44   0.51                                   149    *        0        0.05   0.46   0.49                                   150    *        0        0.05   0.48   0.47                                   151    *        0        0.05   0.50   0.45                                   152    *        0        0.10   0.44   0.46                                   153    *        0        0.10   0.46   0.44                                   154    *        0        0.10   0.48   0.42                                   155    *        0        0.10   0.50   0.40                                   ______________________________________                                    

Each plane of the sample was fitted with a silver electrode by stovingand then polarized in an insulating oil by applying a DC voltage of3.0 - 4.0 KV/mm. After the poling treatment, the sample was kept in adrier for 1 hour at 150°C to carry out the first heat aging, cooled toroom temperature and then kept again in the drier under the sameconditions for 1 hour to carry out the second heat aging.

The heat aging is usually made just after the poling treatment in orderto stabilize the electromechanical coupling coefficient of the ceramicsso that the results after the second heat aging show the heat agingcharacteristics of the ceramics.

The measurements of the piezoelectric characteristics of the sampleswere made just after each heat aging to evaluate the thermostabilitythereof. The dielectric constant (ε_(s)) was measured with a capacitancebridge, and the electromechanical coupling coefficient (kp) and themechanical quality factor (Qm) were measured with the IRE standardcircuits. Results are shown in Table 2 in which the results after thefirst heat aging are listed in the columns indicated by (1) and thoseafter the second heat aging are listed in the columns indicated by (2).

The change rate of electromechanical coupling coefficient is given bythe following equation: ##EQU1##

The negative value of the change rate in Table 2 means that the value ofthe electromechanical coupling coefficient (kp) was increased by thesecond heat aging.

Results for samples Nos. 1 to 12 were excluded from Table 2 since theyhave relatively high values of the mechanical quality factor (Qm > 140)and show little changes in their piezoelectric characteristics such asdielectric constant, electromechanical coupling coefficient andmechanical quality factor. Results for samples Nos. 101 to 108 were alsoexcluded from the table since sintered bodies thereof were neverobtained and the resulant products exhibit no piezoelectriccharacteristics.

Reference samples of a soft type were prepared in the same manner asmentioned above. All of the reference samples consist of the compositionof a system 0.48PbTiO₃ - 0.52PbZrO₃ containing 1 wt % of Nb₂ O₅. Themeasurements of the electromechanical coupling coefficient of thesereference samples were made after each heat aging. Results are shown inTable 3 in which the results after the first heat aging are summarizedin the column indicated by (1) and those after the second heat aging aresummarized in the column indicated by (2). The values in the respectivecolumns (1) and (2) are the maximum and minimum values of the resultsfor five samples. The minimum change rate was obtained by using themaximum value in the column (2) and the minimun value in the column (1).The maximum change rate was obtained by using the maximum value in thecolumn (1) and the minimum value in the column (2).

                                      Table 2                                     __________________________________________________________________________          Dielectric                                                                            Electro-Mechanical                                                                          Mechanical                                        Constant                                                                            Coupling Coefficient                                                                  Quality Factor                                                  Sample                                                                              ε.sub.s                                                                       Kp (%)        Qm                                                                      Change                                                  No.   (1) (2) (1) (2) Rate(%)                                                                             (1) (2)                                           __________________________________________________________________________    1  *  601 --  36.8                                                                              --  --    188 --                                            2  *  704 --  44.0                                                                              --  --    177 --                                            3  *  1366                                                                              --  46.5                                                                              --  --    163 --                                            4  *  989 --  27.8                                                                              --  --    182 --                                            5  *  577 --  38.3                                                                              --  --    202 --                                            6  *  686 --  45.7                                                                              --  --    184 --                                            7  *  1406                                                                              --  46.6                                                                              --  --    170 --                                            8  *  947 --  26.7                                                                              --  --    177 --                                            9  *  605 --  39.0                                                                              --  --    183 --                                            10 *  758 --  46.4                                                                              --  --    194 --                                            11 *  1361                                                                              --  38.6                                                                              --  --    143 --                                            12 *  1028                                                                              --  31.7                                                                              --  --    173 --                                            13 A  641 634 22.3                                                                              21.1                                                                              5.4   98  98                                            14 B  635 629 29.7                                                                              29.3                                                                              1.3   103 105                                           15    643 632 50.3                                                                              48.5                                                                              3.6   152 149                                           16    1033                                                                              1021                                                                              31.2                                                                              30.7                                                                              1.6   99  108                                           17    701 677 45.9                                                                              43.8                                                                              4.6   143 153                                           18    1153                                                                              1113                                                                              35.6                                                                              33.0                                                                              7.3   86  88                                            19    709 708 47.8                                                                              46.4                                                                              2.9   123 137                                           20    1243                                                                              1235                                                                              39.3                                                                              37.2                                                                              5.3   89  96                                            21 C  708 702 33.2                                                                              31.2                                                                              6.0   100 103                                           22 F  731 735 32.1                                                                              27.5                                                                              14.3  111 115                                           23 D  1018                                                                              1021                                                                              25.3                                                                              21.8                                                                              13.8  128 137                                           24 E  1103                                                                              1121                                                                              24.1                                                                              23.3                                                                              3.3   126 126                                           25 A  613 600 25.4                                                                              22.2                                                                              12.6  89  83                                            26 B  597 598 23.1                                                                              20.3                                                                              12.1  82  85                                            27    622 626 32.1                                                                              32.4                                                                              -0.9  94  116                                           28    766 788 33.5                                                                              33.5                                                                              0.0   78  94                                            29    966 959 19.2                                                                              22.0                                                                              -14.6 87  93                                            30    761 753 18.9                                                                              20.0                                                                              -5.8  81  88                                            31    672 661 49.5                                                                              50.5                                                                              -2.0  99  99                                            32    826 807 58.0                                                                              52.5                                                                              9.5   86  84                                            33    1556                                                                              1556                                                                              45.7                                                                              46.0                                                                              -0.7  81  85                                            34    1077                                                                              1068                                                                              33.8                                                                              33.7                                                                              0.3   78  93                                            35    788 777 56.8                                                                              54.4                                                                              4.2   83  90                                            36    994 995 66.5                                                                              69.0                                                                              -3.8  82  82                                            37    1667                                                                              1689                                                                              56.1                                                                              55.5                                                                              1.1   88  91                                            38    1228                                                                              1223                                                                              43.7                                                                              43.9                                                                              -0.5  97  99                                            39    795 783 57.2                                                                              54.3                                                                              5.1   84  90                                            40    994 990 65.8                                                                              62.0                                                                              5.8   76  84                                            41    1672                                                                              1658                                                                              57.8                                                                              56.1                                                                              2.9   79  85                                            42    1267                                                                              1247                                                                              44.5                                                                              44.0                                                                              1.1   90  98                                            43    878 857 56.0                                                                              52.6                                                                              6.1   81  90                                            44    1207                                                                              1200                                                                              66.0                                                                              62.0                                                                              6.1   71  80                                            45    1685                                                                              1663                                                                              56.0                                                                              54.5                                                                              2.7   73  79                                            46    1275                                                                              1261                                                                              46.5                                                                              46.0                                                                              1.1   87  95                                            47    890 897 44.2                                                                              44.0                                                                              0.5   83  85                                            48    1231                                                                              1245                                                                              46.3                                                                              45.1                                                                              2.6   80  82                                            49    1701                                                                              1693                                                                              50.3                                                                              48.9                                                                              2.8   73  77                                            50    1258                                                                              1249                                                                              43.2                                                                              42.1                                                                              2.5   85  89                                            51 C  683 664 21.1                                                                              20.1                                                                              4.7   88  92                                            52 F  813 795 27.5                                                                              26.5                                                                              3.6   93  99                                            53 D  962 978 29.0                                                                              28.9                                                                              0.3   100 102                                           54 E  998 1001                                                                              26.3                                                                              25.5                                                                              3.0   100 97                                            55    596 592 23.6                                                                              23.8                                                                              0.8   92  95                                            56    389 394 25.9                                                                              26.3                                                                              1.5   103 100                                           57    604 600 39.6                                                                              39.5                                                                              0.3   97  81                                            58    678 679 48.2                                                                              48.2                                                                              0.0   87  92                                            59    875 880 55.0                                                                              55.1                                                                              0.2   68  82                                            60    1544                                                                              1549                                                                              45.3                                                                              45.7                                                                              0.9   60  77                                            61    1057                                                                              1058                                                                              33.6                                                                              34.0                                                                              1.2   66  82                                            62    682 681 49.0                                                                              48.8                                                                              0.4   98  95                                            63    730 726 44.1                                                                              44.0                                                                              0.2   80  79                                            64    713 699 57.9                                                                              58.0                                                                              0.2   90  89                                            65    835 835 61.6                                                                              61.2                                                                              0.6   78  81                                            66    905 900 61.7                                                                              61.8                                                                              0.2   84  80                                            67    1581                                                                              1610                                                                              63.7                                                                              63.5                                                                              0.3   60  76                                            68    1725                                                                              1737                                                                              54.9                                                                              55.9                                                                              1.8   82  68                                            69    1393                                                                              1396                                                                              46.0                                                                              46.1                                                                              0.2   74  83                                            70    1292                                                                              1353                                                                              42.4                                                                              43.2                                                                              1.9   90  85                                            71    1067                                                                              1067                                                                              36.7                                                                              36.8                                                                              0.3   95  96                                            72    911 913 30.5                                                                              31.0                                                                              1.6   87  107                                           73    733 730 48.5                                                                              47.7                                                                              1.6   84  92                                            74    837 836 62.0                                                                              60.5                                                                              2.4   71  83                                            75    1115                                                                              1139                                                                              66.4                                                                              65.2                                                                              1.8   58  74                                            76    1632                                                                              1638                                                                              60.0                                                                              59.0                                                                              1.7   84  77                                            77    1272                                                                              1266                                                                              46.6                                                                              46.4                                                                              0.4   79  89                                            78    800 804 37.1                                                                              36.8                                                                              0.8   75  88                                            79    842 851 56.8                                                                              54.6                                                                              3.8   79  90                                            80    850 854 57.6                                                                              56.8                                                                              1.4   86  88                                            81    979 999 63.1                                                                              60.9                                                                              3.5   68  77                                            82    1124                                                                              1135                                                                              60.9                                                                              59.7                                                                              2.0   76  69                                            83    1676                                                                              1707                                                                              70.0                                                                              68.2                                                                              2.9   58  73                                            84    1612                                                                              1680                                                                              44.3                                                                              43.6                                                                              1.6   66  75                                            85    1582                                                                              1583                                                                              57.0                                                                              56.7                                                                              0.5   68  86                                            86    1270                                                                              1276                                                                              45.9                                                                              44.0                                                                              4.1   95  84                                            87    1202                                                                              1199                                                                              44.5                                                                              44.5                                                                              0.0   84  100                                           88    1061                                                                              1060                                                                              40.1                                                                              40.3                                                                              0.5   90  107                                           89    862 869 34.9                                                                              34.6                                                                              0.9   94  98                                            90    934 948 54.5                                                                              51.9                                                                              4.8   74  86                                            91    1454                                                                              1507                                                                              53.4                                                                              55.0                                                                              3.0   70  74                                            92    1772                                                                              1788                                                                              55.4                                                                              54.8                                                                              1.1   73  82                                            93    1325                                                                              1332                                                                              42.3                                                                              42.1                                                                              0.5   77  93                                            94    1141                                                                              1138                                                                              44.7                                                                              42.4                                                                              5.1   85  92                                            95    1551                                                                              1549                                                                              51.9                                                                              48.5                                                                              6.6   73  78                                            96    1440                                                                              1415                                                                              37.7                                                                              36.1                                                                              4.2   85  89                                            97    1100                                                                              1087                                                                              32.7                                                                              33.1                                                                              1.2   100 100                                           98    557 561 29.4                                                                              29.1                                                                              1.0   93  90                                            99    572 570 20.8                                                                              20.7                                                                              0.5   112 111                                           100   964 967 35.1                                                                              35.0                                                                              0.3   82  85                                            101   825 821 22.6                                                                              22.4                                                                              0.9   106 107                                           102                                                                              A  607 603 24.5                                                                              22.4                                                                              8.6   92  81                                            103                                                                              B  632 615 27.3                                                                              23.8                                                                              12.8  83  89                                            104   574 590 50.8                                                                              51.5                                                                              -1.4  91  97                                            105   850 882 62.5                                                                              63.5                                                                              -1.6  77  74                                            106   1397                                                                              1388                                                                              43.2                                                                              43.3                                                                              -0.2  37  55                                            107   810 812 27.5                                                                              29.5                                                                              -7.3  58  74                                            108   777 771 59.7                                                                              57.5                                                                              3.7   88  91                                            109   1048                                                                              1062                                                                              69.0                                                                              65.0                                                                              5.8   81  81                                            110   1639                                                                              1635                                                                              60.6                                                                              58.5                                                                              3.5   87  89                                            111   1230                                                                              1221                                                                              45.3                                                                              45.0                                                                              0.7   97  99                                            112   955 944 52.5                                                                              48.2                                                                              8.2   82  88                                            113   1324                                                                              1319                                                                              50.5                                                                              49.0                                                                              3.0   69  73                                            114   1508                                                                              1490                                                                              41.5                                                                              42.0                                                                              -1.2  71  76                                            115   1181                                                                              1178                                                                              33.3                                                                              33.5                                                                              -0.6  84  84                                            116   895 933 44.0                                                                              42.7                                                                              3.0   77  80                                            117   1280                                                                              1344                                                                              66.6                                                                              63.0                                                                              5.4   62  64                                            118   1630                                                                              1668                                                                              53.0                                                                              52.2                                                                              1.5   72  75                                            119   1266                                                                              1286                                                                              43.7                                                                              43.1                                                                              1.4   83  88                                            120   1058                                                                              1096                                                                              40.2                                                                              38.3                                                                              4.7   77  80                                            121   1533                                                                              1519                                                                              50.0                                                                              48.5                                                                              3.0   75  72                                            122   1341                                                                              1359                                                                              44.0                                                                              43.0                                                                              2.3   81  84                                            123   1030                                                                              1042                                                                              37.2                                                                              36.8                                                                              1.1   90  96                                            124   1108                                                                              1123                                                                              36.2                                                                              35.0                                                                              3.3   73  75                                            125   1611                                                                              1638                                                                              45.9                                                                              44.3                                                                              3.5   70  77                                            126   1404                                                                              1429                                                                              38.8                                                                              38.0                                                                              2.1   78  81                                            127   1129                                                                              1105                                                                              32.5                                                                              31.5                                                                              3.1   82  85                                            128                                                                              C  739 721 31.2                                                                              29.6                                                                              5.1   79  82                                            129                                                                              F  853 831 33.3                                                                              30.2                                                                              9.3   87  93                                            130                                                                              D.sub.1                                                                          973 999 29.9                                                                              27.3                                                                              8.7   83  85                                            131                                                                              E.sub.1                                                                          1003                                                                              1012                                                                              28.3                                                                              26.5                                                                              6.4   92  98                                            132                                                                              A  543 534 22.1                                                                              21.4                                                                              3.2   93  70                                            133                                                                              B  421 401 25.6                                                                              24.8                                                                              3.1   71  75                                            134   795 789 59.3                                                                              56.5                                                                              4.7   88  90                                            135   1238                                                                              1226                                                                              43.2                                                                              42.3                                                                              2.1   83  99                                            136   979 962 61.1                                                                              50.0                                                                              2.2   89  88                                            137   1121                                                                              1180                                                                              38.0                                                                              37.9                                                                              0.3   87  86                                            138                                                                              C  893 973 48.2                                                                              46.1                                                                              4.4   86  87                                            139                                                                              F.sub.2                                                                          1099                                                                              1121                                                                              45.0                                                                              42.2                                                                              6.2   81  83                                            140   621 635 25.0                                                                              24.6                                                                              1.6   80  78                                            141   731 741 26.2                                                                              25.1                                                                              4.2   75  81                                            142                                                                              D.sub.2                                                                          997 989 24.3                                                                              23.2                                                                              4.5   70  76                                            143                                                                              E.sub.2                                                                          1031                                                                              1005                                                                              29.5                                                                              27.3                                                                              7.5   80  87                                            144                                                                              *  878 869 56.5                                                                              56.0                                                                              0.9   88  90                                            145                                                                              *  1252                                                                              1267                                                                              68.0                                                                              63.0                                                                              7.4   79  83                                            146                                                                              *  1601                                                                              1590                                                                              54.5                                                                              53.5                                                                              1.8   84  88                                            147                                                                              *  1254                                                                              1237                                                                              46.0                                                                              46.0                                                                              0.0   96  99                                            148                                                                              *  --  --  --  --  --    --  --                                            149                                                                              *  --  --  --  --  --    --  --                                            150                                                                              *  --  --  --  --  --    --  --                                            151                                                                              *  --  --  --  --  --    --  --                                            152                                                                              *  --  --  --  --  --    --  --                                            153                                                                              *  --  --  --  --  --    --  --                                            154                                                                              *  --  --  --  --  --    --  --                                            155                                                                              *  --  --  --  --  --    --  --                                            __________________________________________________________________________

                  Table 3                                                         ______________________________________                                        Electromechanical coupling                                                                         Change Rate                                              coefficient kp (%)   (%)                                                      (1)        (2)                                                                ______________________________________                                        68 - 70    52 - 55       19 - 26                                              ______________________________________                                    

As will be evident from Tables 2 and 3, the ceramic compositions of theinvention are scarcely changed in their piezoelectric characteristics bythe repetition of the heat aging whereas the ceramic composition of thereference samples has a tendency to cause the deterioration of theelectromechanical coupling coefficient by the repetition of the heataging. Thus, it will be noted that the ceramic compositions of thisinvention are superior in stability to the ceramic composition of thereference samples.

The stability of the piezoelectric characteristics is very important incases where the ceramic compositions are applied to mechanical ceramicfilters, ceramic resonators, oscillators and the like.

In order to examine the utility of the ceramic compositions of theinvention, the ceramic composition are applied to resonators in thefollowing manner.

The disk obtained by the above mentioned preparation methos was groundso as to have a thickness of 0.2 mm. The thus obtained thin disk wasfitted with a silver electrode layer on each plane thereof and thenpolarized in the same manner as mentioned above. After a polingtreatment, the thin disk was provided with an opposite electrode on eachplane thereof to complete the preparation of an energy trapped moderesonator having an intermediate frequency of 10.7 MHz. The resonatorwas coated by a well-known dip coating method.

The measurements of antiresonance and resonance frequencies of theresonator were made before and after the dip coating, whereby anexamination was made as to how the difference Δf (= fa - fo) between theantiresonance and resonance frequencies is affected by the heat and theclamping force caused by the hardening of the paints, both of which areapplied to the resonator during dip coating. The differences Δf beforeand after dip coating are shown in Table 4.

                                      Table 4                                     __________________________________________________________________________    Δf (KHz)         Δf (KHz)                                         Sample                                                                              Before dip                                                                          After dip                                                                           Sample                                                                             Before dip                                                                          After dip                                        No.   coating                                                                             coating                                                                             No.  coating                                                                             coating                                          __________________________________________________________________________    1     347   364   36   673   675                                              2     453   461   37   611   621                                              3     450   446   38   510   502                                              4     150   134   39   631   626                                              5     433   450   40   668   671                                              6     511   523   41   676   686                                              7     498   507   42   530   521                                              8     135   143   43   560   567                                              9     492   481   44   607   612                                              10    573   585   45   638   649                                              11    500   523   46   508   514                                              12    210   249   47   465   467                                              13    --    --    48   478   480                                              14    180   175   49   515   518                                              15    515   514   50   449   446                                              16    216   212   51   --    --                                               17    461   465   52   --    --                                               18    253   270   53   170   165                                              19    492   494   54   --    --                                               20    373   366   55   --    --                                               21    233   224   56   --    --                                               22    119   127   57   293   309                                              23    --    --    58   436   456                                              24    --    --    59   515   546                                              25    --    --    60   451   460                                              26    --    --    61   126   195                                              27    253   247   62   459   471                                              28    310   312   63   505   534                                              29    231   249   64   505   526                                              30    --    --    65   535   565                                              31    600   601   66   545   558                                              32    688   693   67   572   575                                              33    661   660   68   586   596                                              34    331   334   69   469   494                                              35    607   608   70   424   424                                              71    282   290   106  651   656                                              72    265   270   107  230   245                                              73    435   460   108  559   561                                              74    540   563   109  639   648                                              75    569   574   110  664   664                                              76    597   598   111  500   509                                              77    444   436   112  500   501                                              78    357   367   113  415   414                                              79    465   471   114  450   447                                              80    509   518   115  350   354                                              81    514   538   116  300   303                                              82    529   533   117  635   640                                              83    601   604   118  577   568                                              84    450   451   119  500   499                                              85    567   560   120  389   400                                              86    450   451   121  542   540                                              87    427   419   122  501   506                                              88    328   318   123  211   220                                              89    259   250   124  312   315                                              90    467   464   125  468   471                                              91    541   534   126  379   382                                              92    561   561   127  218   233                                              93    460   460   128  172   183                                              94    417   377   129  199   200                                              95    498   472   130  117   122                                              96    392   390   131  --    --                                               97    228   217   132  --    --                                               98    207   200   133  --    --                                               99    --    --    134  569   575                                              100   234   231   135  450   448                                              101   --    --    136  518   527                                              102   --    --    137  361   380                                              103   --    --    138  472   490                                              104   580   578   139  400   448                                              105   668   673   140  --    --                                               141   --    --                                                                142   --    --                                                                143   121   112                                                               144   523   532                                                               145   549   558                                                               146   570   572                                                               147   510   509                                                               148   --    --                                                                149   --    --                                                                150   --    --                                                                151   --    --                                                                152   --    --                                                                153   --    --                                                                154   --    --                                                                155   --    --                                                                Reference                                                                     Sample                                                                              680   500                                                               __________________________________________________________________________

From this table, it will be seen that the ceramic compositions of theinvention are scarcely influenced by the processing whereas the ceramiccomposition of the reference sample is greatly influenced. Thus, theceramic compositions of the invention are useful for use as materialsfor resonators, mechanical ceramic filters and the like.

Experiments with respect to the samples having a low electromechanicalcoupling coefficient less than 25% were omitted since it was difficultto prepare the energy trapped mode resonators for 10.7 MHz.

Some of the representatives of the ceramic compositions of the inventionwere examined as to how the temperature coefficients (TC) of theantiresonance and resonance frequencies in a temperature range of -20°Cto + 80°C vary with the change of the ratio of PbTiO₃ /PbZrO₃ when themol fraction of the component Pb(Sn.sub.αSb₁ ₋.sub.α)O₃ is fixed. Theresults are shown in FIGS. 2 through 6.

The temperature coefficients(TC) were obtained by use of the followingequations: ##EQU2##

FIG. 7 shows the changes of temperature coefficients (TC) when α = 1.00and x = 0.05 as a function of the mol fractions of PbTiO₃ and PbZrO₃.

In FIGS. 2 through 7, the solid line shows the result for theantiresonance frequency and the broken line shows the result for theresonance frequency. The positive and negative signs (+) (-) of TC inthese figures have respectively the following meanings. The positivesign (+) means that the value of fomax (or famax) is found at atemperature higher than the room temperature (+20°C) or that the valueof fomin (or famin) is found at a temperature lower than the roomtemperature (+20°C). The negative sign (-) has the opposite meaning ofthe positive sign.

From FIGS. 2 through 6, it will be seen that good points of thetemperature coefficent are present in a wide compositional area wherethe mol fraction of PbZrO₃ ranges from 0.46 to 0.51. This shows thataccording to the present invention the piezoelectric ceramic materialshaving a good temperature coefficient can be obtained with ease whendesigning the filters, oscillators and the like having any desiredpiezoelectric characteristics such as ε_(s), kp and Qm. On the contrary,the ceramic compositions beyond the limits of the compositional area ofthis invention (i.e. α = 1) have large values on the positive side, ascan be seen from FIG. 7. It is therefore impossible to select thecomposition having good temperature coefficient from these compositions.

FIG. 8 shows the relation between the degree of sintering and thecontents of Sn and Sb. In this figure, the symbol () shows thecomposition which was converted into a fine structural sintered body andthe symbol (□) shows the composition which was never converted into asintered body.

From this figure, it will be seen that the compositional area where thefine structural sintered body can be obtained decreases with thedecrease of the content of Sn. It will be also seen that if the contentof Sb is more than 5 atomic percent when the content of Sn is zero, thefine structural sintered body is never obtained.

The area of the present composition has been described as being in thepolygonal area defined by the points A, B, C, D, E and F in FIG. 1 forthe following reasons. If the content of Pb(Sn.sub.αSb₁ ₋.sub.α)O₃ isless than 1 mol percent when 1/4 ≦ α ≦ 3/4, the temperature coefficientof the composition becomes great. Further, if the content ofPb(Sn.sub.αSb₁ ₋.sub.α)O₃ is more than 25 mol percent when 1/2 ≦ α ≦3/4, or more than 20 mol percent when 1/3 ≦ α < 1/2, or more than 15 molpercent when 1/4 ≦ α < 1/3, the electromechanical coupling coefficientof the composition becomes less than 20% and varies greatly by the heataging. In addition, if the content of PbTiO₃ is more than 60 mol percentor if the content of PbZrO₃ is more than 69 mol percent, theelectromechanical coupling coefficient of the composition becomes lessthan 20 %.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications are intended to be included within the scope of thefollowing claims.

What is claimed is:
 1. A ferroelectric ceramic composition of theternary system Pb(Sn.sub.αSb₁ ₋₃₀₁)O₃ --PbTiO₃ --PbZrO₃ comprising asolid solution represented by the general formula:

    xPb(Sn.sub.αSb.sub.1.sub.-.sub.α O.sub.3)-yPbTiO.sub.3 -zPbZrO.sub.3

wherein x + y + z = 1.00 and 1/2 ≦ α ≦ 3/4,said composition being in apolygonal area defined by the points A, B, C, D, E and F in FIG. 1, thesets of mole fractions of the three components at said points being asfollows:x y z______________________________________0.01 0.60 0.390.010.30 0.690.15 0.25 0.600.25 0.25 0.500.25 0.50 0.250.15 0.600.25______________________________________
 2. The ferroelectric ceramiccomposition according to claim 1 wherein α is 3/4.
 3. The ferroelectricceramic composition according to claim 1 wherein α is 2/3.
 4. Theferroelectric ceramic composition according to claim 1 wherein α is 1/2.5. A ferroelectric ceramic composition of the ternary systemPb(Sn.sub.αSb₁ ₋.sub.α)O₃ --PbTiO₃ --PbZrO₃ comprising a solid solutionrepresented by the general formula:

    xPb(Sn.sub.1/4Sb.sub.3/4O.sub.3)--yPbTiO.sub.3 --zPbZrO.sub.3

wherein x + y + z = 1.00, said composition being in a polygonal areadefined by the points A, B, C, D₂, E₂ and F in FIG. 1, the sets of molefractions of the three components at said points being as follows:x yz______________________________________0.01 0.60 0.390.01 0.30 0.690.150.25 0.600.15 0.35 0.500.15 0.50 0.350.15 0.600.25______________________________________